Method and apparatus for production of three-dimensional objects by stereolithography

ABSTRACT

A system for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed at a selected surface of a fluid medium capable of altering its physical state in response to appropriate synergistic stimulation by impinging radiation, particle bombardment or chemical reaction, successive adjacent laminae, representing corresponding successive adjacent cross-sections of the object, being automatically formed and integrated together to provide a step-wise laminar buildup of the desired object, whereby a three-dimensional object is formed and drawn from a substantially planar surface of the fluid medium during the forming process.

This is a continuation of Ser. No. 08/299,878, filed on Sep. 1, 1994,now abandoned; which is a divisional of Ser. No. 07/967,303, filed Oct.20, 1992, now U.S. Pat. No. 5,344,298; which is a continuation of Ser.No. 07/749,125, filed Aug. 23, 1991, now U.S. Pat. No. 5,174,943; whichis a continuation of Ser. No. 07/637,999, filed Jan. 4, 1991, nowabandoned; which is a continuation of Ser. No. 07/493,498, filed Mar.14, 1990, now abandoned; which is a divisional of Ser. No. 07/340,894,filed Apr. 19, 1989, now U.S. Pat. No. 4,929,402; which is acontinuation of Ser. No. 07/161,346, filed Feb. 19, 1988, now abandoned;which is a continuation of Ser. No. 06/792,979, filed Dec. 9, 1985, nowabandoned; which is a divisional of Ser. No. 06/638,905, filed Aug. 8,1984, now U.S. Pat. No. 4,575,330.

BACKGROUND OF THE INVENTION

This invention relates generally to improvements in methods andapparatus for forming three-dimensional objects from a fluid medium and,more particularly, to stereolithography involving the application oflithographic techniques to production of three-dimensional objects,whereby such objects can be formed rapidly, reliably, accurately andeconomically.

It is common practice in the production of plastic parts and the like tofirst design such a part and then painstakingly produce a prototype ofthe part, all involving considerable time, effort and expense. Thedesign is then reviewed and, oftentimes, the laborious process is againand again repeated until the design has been optimized. After designoptimization, the next step is production. Most production plastic partsare injection molded. Since the design time and tooling costs are veryhigh, plastic parts are usually only practical in high volumeproduction. While other processes are available for the production ofplastic parts, including direct machine work, vacuum-forming and directforming, such methods are typically only cost effective for short runproduction, and the parts produced are usually inferior in quality tomolded parts.

In recent years, very sophisticated techniques have been developed forgenerating three-dimensional objects within a fluid medium which isselectively cured by beams of radiation brought to selective focus atprescribed intersection points within the three-dimensional volume ofthe fluid medium. Typical of such three-dimensional systems are thosedescribed in U.S. Pat. Nos. 4,041,476, 4,078,229, 4,238,840 and4,288,861. All of these systems rely upon the buildup of synergisticenergization at selected points deep within the fluid volume, to theexclusion of all other points in the fluid volume, using a variety ofelaborate multibeam techniques. In this regard, the various approachesdescribed in the prior art include the use of a pair of electromagneticradiation beams directed to intersect at specified coordinates, whereinthe various beams may be of the same or differing wavelengths, or wherebeams are used sequentially to intersect the same points rather thansimultaneously, but in all cases only the beam intersection points arestimulated to sufficient energy levels to accomplish the necessarycuring process for forming a three-dimensional object within the volumeof the fluid medium. Unfortunately, however, such three-dimensionalforming systems face a number of problems with regard to resolution andexposure control. The loss of radiation intensity and image formingresolution of the focused spots as the intersections move deeper intothe fluid medium create rather obvious complex control situations.Absorption, diffusion, dispersion and diffraction all contribute to thedifficulties of working deep within the fluid medium on any economicaland reliable basis.

Yet there continues to be a long existing need in the design andproduction arts for the capability of rapidly and reliably moving fromthe design stage to the prototype stage and to ultimate production,particularly moving directly from computer designs for such plasticparts to virtually immediate prototypes and the facility for large scaleproduction on an economical and automatic basis.

Accordingly, those concerned with the development and production ofthree-dimensional plastic objects and the like have long recognized thedesirability for further improvement in more rapid, reliable, economicaland automatic means which would facilitate quickly moving from a designstage to the prototype stage and to production, while avoiding thecomplicated focusing, alignment and exposure problems of the prior artthree dimensional production systems. The present invention clearlyfulfills all of these needs.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the present invention provides a new andimproved system for generating a three-dimensional object by formingsuccessive, adjacent, cross-sectional laminae of that object at thesurface of a fluid medium capable of altering its physical state inresponse to appropriate synergistic stimulation, the successive laminaebeing automatically integrated as they are formed to define the desiredthree-dimensional object.

In a presently preferred embodiment, by way of example and notnecessarily by way of limitation, the present invention harnesses theprinciples of computer generated graphics in combination withstereolithography, i.e., the application of lithographic techniques tothe production of three dimensional objects, to simultaneously executecomputer aided design (CAD) and computer aided manufacturing (CAM) inproducing three-dimensional objects directly from computer instructions.The invention can be applied for the purposes of sculpturing models andprototypes in a design phase of product development, or as amanufacturing system, or even as a pure art form.

"Stereolithography" is a method and apparatus for making solid objectsby successively "printing" thin layers of a curable material, e.g., a UVcurable material, one on top of the other. A programmed movable spotbeam of UV light shining on a surface or layer of UV curable liquid isused to form a solid cross-section of the object at the surface of theliquid. The object is then moved, in a programmed manner, away from theliquid surface by the thickness of one layer, and the next cross-sectionis then formed and adhered to the immediately preceding layer definingthe object. This process is continued until the entire object is formed.

Essentially all types of object forms can be created with the techniqueof the present invention. Complex forms are more easily created by usingthe functions of a computer to help generate the programmed commands andto then send the program signals to the stereolithographic objectforming subsystem.

Of course, it will be appreciated that other forms of appropriatesynergistic stimulation for a curable fluid medium, such as particlebombardment (electron beams and the like), chemical reactions byspraying materials through a mask or by ink jets, or impinging radiationother than ultraviolet light, may be used in the practice of theinvention without departing from the spirit and scope of the invention.

By way of example, in the practice of the present invention, a body of afluid medium capable of solidification in response to prescribedstimulation is first appropriately contained in any suitable vessel todefine a designated working surface of the fluid medium at whichsuccessive cross-sectional laminae can be generated. Thereafter, anappropriate form of synergistic stimulation, such as a spot of UV lightor the like, is applied as a graphic pattern at the specified workingsurface of the fluid medium to form thin, solid, individual layers atthat surface, each layer representing an adjacent cross-section of thethree-dimensional object to be produced. Superposition of successiveadjacent layers on each other is automatically accomplished, as they areformed, to integrate the layers and define the desired three-dimensionalobject. In this regard, as the fluid medium cures and solid materialforms as a thin lamina at the working surface, a suitable platform towhich the first lamina is secured is moved away from the working surfacein a programmed manner by any appropriate actuator, typically all underthe control of a micro-computer or the like. In this way, the solidmaterial that was initially formed at the working surface is moved awayfrom that surface and new liquid flows into the working surfaceposition. A portion of this new liquid is, in turn, converted to solidmaterial by the programmed UV light spot to define a new lamina, andthis new lamina adhesively connects to the material adjacent to it,i.e., the immediately preceding lamina. This process continues until theentire three-dimensional object has been formed. The formed object isthen removed from the container and the apparatus is ready to produceanother object, either identical to the first object or an entirely newobject generated by a computer or the like.

The stereolithographic method and apparatus of the present invention hasmany advantages over currently used methods for producing plasticobjects. The method of the present invention avoids the need ofproducing design layouts and drawings, and of producing tooling drawingsand tooling. The designer can work directly with the computer and astereolithographic device, and when he is satisfied with the design asdisplayed on the output screen of the computer, he can fabricate a partfor direct examination. If the design has to be modified, it can beeasily done through the computer, and then another part can be made toverify that the change was correct. If the design calls for severalparts with interacting design parameters, the method of the inventionbecomes even more useful because all of the part designs can be quicklychanged and made again so that the total assembly can be made andexamined, repeatedly if necessary.

After the design is complete, part production can begin immediately, sothat the weeks and months between design and production are avoided.Ultimate production rates and parts costs should be similar to currentinjection molding costs for short run production, with even lower laborcosts than those associated with injection molding. Injection molding iseconomical only when large numbers of identical parts are required.Stereolithography is useful for short run production because the needfor tooling is eliminated and production set-up time is minimal.Likewise, design changes and custom parts are easily provided using thetechnique. Because of the ease of making parts, stereolithography canallow plastic parts to be used in many places where metal or othermaterial parts are now used. Moreover, it allows plastic models ofobjects to be quickly and economically provided, prior to the decisionto make more expensive metal or other material parts.

Hence, the stereolithographic method and apparatus of the presentinvention satisfies a long existing need for a CAD and CAM systemcapable of rapidly, reliably, accurately and economically designing andfabricating three-dimensional plastic parts and the like.

The above and other objects and advantages of this invention will beapparent from the following more detailed description when taken inconjunction with the accompanying drawings of illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 2 are flow charts illustrating the basic conceptsemployed in practicing the method of stereolithography of the presentinvention;

FIG. 3 is a combined block diagram, schematic and elevational sectionalview of a presently preferred embodiment of a system for practicing theinvention;

FIG. 4 is an elevational sectional view of a second embodiment of astereolithography system for the practice of the invention;

FIG. 5 is an elevational sectional view, illustrating a third embodimentof the present invention;

FIG. 6 is an elevational sectional view illustrating still anotherembodiment of the present invention; and

FIGS. 7 and 8 are partial, elevational sectional views, illustrating amodification of the stereolithographic system of FIG. 3 to incorporatean elevator platform with multiple degrees of freedom.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, FIGS. 1 and 2 are flow chartsillustrating the basic method and system of the present invention forgenerating three-dimensional objects by means of stereolithography.

Many liquid state chemicals are known which can be induced to change tosolid state polymer plastic by irradiation with ultraviolet light (UV)or other forms of synergistic stimulation such as electron beams,visible or invisible light, reactive chemicals applied by ink jet or viaa suitable mask. UV curable chemicals are currently used as ink for highspeed printing, in processes of coating of paper and other materials, asadhesives, and in other specialty areas.

Lithography is the art of reproducing graphic objects, using varioustechniques. Modern examples include photographic reproduction,xerography, and microlithography, as is used in the production ofmicro-electronics. Computer generated graphics displayed on a plotter ora cathode ray tube are also forms of lithography, where the image is apicture of a computer coded object.

Computer aided design (CAD) and computer aided manufacturing (CAM) aretechniques that apply the abilities of computers to the processes ofdesigning and manufacturing. A typical example of CAD is in the area ofelectronic printed circuit design, where a computer and plotter draw thedesign of a printed circuit board, given the design parameters ascomputer data input. A typical example of CAM is a numericallycontrolled milling machine, where a computer and a milling machineproduce metal parts, given the proper programming instructions. Both CADand CAM are important and are rapidly growing technologies.

A prime object of the present invention is to harness the principles ofcomputer generated graphics, combined with UV curable plastic and thelike, to simultaneously execute CAD and CAM, and to producethree-dimensional objects directly from computer instructions. Thisinvention, referred to as stereolithography, can be used to sculpturemodels and prototypes in a design phase of product development, or as amanufacturing device, or even as an art form.

Referring now to FIG. 1, the stereolithographic method of the presentinvention is broadly outlined. Step 10 in FIG. 1 calls for thegeneration of individual solid laminae representing cross-sections of athree-dimensional object to be formed. Step 11, which inherently occursif Step 10 is performed properly, combines the successively formedadjacent laminae to form the desired three-dimensional object which hasbeen programmed into the system for selective curing. Hence, thestereolithographic system of the present invention generatesthree-dimensional objects by creating a cross-sectional pattern of theobject to be formed at a selected surface of a fluid medium, e.g., a UVcurable liquid or the like, capable of altering its physical state inresponse to appropriate synergistic stimulation such as impingingradiation, electron beam or other particle bombardment, or appliedchemicals (as by ink jet or spraying over a mask adjacent the fluidsurface), successive adjacent laminae, representing correspondingsuccessive adjacent cross-sections of the object, being automaticallyformed and integrated together to provide a step-wise laminar or thinlayer buildup of the object, whereby a three-dimensional object isformed and drawn from a substantially planar or sheet-like surface ofthe fluid medium during the forming process.

The aforedescribed technique is more specifically outlined in theflowchart of FIG. 2, wherein Step 12 calls for containing a fluid mediumcapable of solidification in response to prescribed reactivestimulation. Step 13 calls for application of that stimulation as agraphic pattern at a designated fluid surface to form thin, solid,individual layers at that surface, each layer representing an adjacentcross-section of a three-dimensional object to be produced. It isdesirable to make each such layer as thin as possible during thepractice of the invention in order to maximize resolution and theaccurate reproduction of the three-dimensional object being formed.Hence, the ideal theoretical state would be an object produced only atthe designated working surface of the fluid medium to provide aninfinite number of laminae, each lamina having a cured depth ofapproximately only slightly more than zero thickness. Of course, in thepractical application of the invention, each lamina will be a thinlamina, but thick enough to be adequately cohesive in forming thecross-section and adhering to the adjacent laminae defining othercross-sections of the object being formed.

Step 14 in FIG. 2 calls for superimposing successive adjacent layers orlaminae on each other as they are formed, to integrate the variouslayers and define the desired three-dimensional object. In the normalpractice of the invention, as the fluid medium cures and solid materialforms to define one lamina, that lamina is moved away from the workingsurface of the fluid medium and the next lamina is formed in the newliquid which replaces the previously formed lamina, so that eachsuccessive lamina is superimposed and integral with (by virtue of thenatural adhesive properties of the cured fluid medium) all of the othercross-sectional laminae. Hence, the process of producing suchcross-sectional laminae is repeated over and over again until the entirethree-dimensional object has been formed. The object is then removed andthe system is ready to produce another object which may be identical tothe previous object or may be an entirely new object formed by changingthe program controlling the stereolithographic system.

FIGS. 3-8 of the drawings illustrate various apparatus suitable forimplementing the stereolithographic methods illustrated and described bythe flow charts of FIGS. 1 and 2.

As previously indicated, "Stereolithography" is a method and apparatusfor making solid objects by successively "printing" thin layers of acurable material, e.g., a UV curable material, one on top of the other.A programmed movable spot beam of UV light shining on a surface or layerof UV curable liquid is used to form a solid cross-section of the objectat the surface of the liquid. The object is then moved, in a programmedmanner, away from the liquid surface by the thickness of one layer andthe next cross-section is then formed and adhered to the immediatelypreceding layer defining the object. This process is continued until theentire object is formed.

Essentially all types of object forms can be created with the techniqueof the present invention. Complex forms are more easily created by usingthe functions of a computer to help generate the programmed commands andto then send the program signals to the stereolithographic objectforming subsystem.

A presently preferred embodiment of the stereolithographic system isshown in elevational cross-section in FIG. 3. A container 21 is filledwith a UV curable liquid 22 or the like, to provide a designated workingsurface 23. A programmable source of ultraviolet light 26 or the likeproduces a spot of ultraviolet light 27 in the plane of surface 23. Thespot 27 is movable across the surface 23 by the motion of mirrors orother optical or mechanical elements (not shown) that are a part oflight source 26. The position of the spot 27 on surface 23 is controlledby a computer or other programming device 28. A movable elevatorplatform 29 inside container 21 can be moved up and down selectively,the position of the platform being controlled by the computer 28. As thedevice operates, it produces a three-dimensional object 30 by step-wisebuildup of integrated laminae such as 30a, 30b, 30c.

The surface of the UV curable liquid 22 is maintained at a constantlevel in the container 21, and the spot of UV light 27, or othersuitable form of reactive stimulation, of sufficient intensity to curethe liquid and convert it to a solid material is moved across theworking surface 23 in a programmed manner. As the liquid 22 cures andsolid material forms, the elevator platform 29 that was initially justbelow surface 23 is moved down from the surface in a programmed mannerby any suitable actuator. In this way, the solid material that wasinitially formed is taken below surface 23 and new liquid 22 flowsacross the surface 23. A portion of this new liquid is, in turn,converted to solid material by the programmed UV light spot 27, and thenew material adhesively connects to the material below it. This processis continued until the entire three-dimensional object 30 is formed. Theobject 30 is then removed from the container 21, and the apparatus isready to produce another object. Another object can then be produced, orsome new object can be made by changing the program in the computer 28.

The curable liquid 22, e.g., UV curable liquid, must have severalimportant properties. A) It must cure fast enough with the available UVlight source to allow practical object formation times. B) It must beadhesive, so that successive layers will adhere to each other. C) Itsviscosity must be low enough so that fresh liquid material will quicklyflow across the surface when the elevator moves the object. D) It shouldabsorb UV so that the film formed will be reasonably thin. E) It must bereasonably soluble in some solvent in the liquid state, and reasonablyinsoluble in that same solvent in the solid state, so that the objectcan be washed free of the UV cure liquid and partially cured liquidafter the object has been formed. F) It should be as non-toxic andnon-irritating as possible.

The cured material must also have desirable properties once it is in thesolid state. These properties depend on the application involved, as inthe conventional use of other plastic materials. Such parameters ascolor, texture, strength, electrical properties, flammability, andflexibility are among the properties to be considered. In addition, thecost of the material will be important in many cases.

The UV curable material used in the presently preferred embodiment of aworking stereolithograph (e.g., FIG. 3) is Potting Compound 363, amodified acrylate, made by Loctite Corporation of Newington, Conn. Aprocess to make a typical UV curable material is described in U.S. Pat.No. 4,100,141, entitled Stabilized Adhesive and Curing Compositions.

The light source 26 produces the spot 27 of UV light small enough toallow the desired object detail to be formed, and intense enough to curethe UV curable liquid being used quickly enough to be practical. Thesource 26 is arranged so it can be programmed to be turned off and on,and to move, such that the focused spot 27 moves across the surface 23of the liquid 22. Thus, as the spot 27 moves, it cures the liquid 22into a solid, and "draws" a solid pattern on the surface in much thesame way a chart recorder or plotter uses a pen to draw a pattern onpaper.

The light source 26 for the presently preferred embodiment of astereolithograph is made using a 350 watt mercury short arc lamp in ahousing, with the light output of the housing focused on the end of a 1mm diameter UV transmitting fiber optic bundle (not shown). The end ofthe bundle next to the lamp is water cooled, and there is anelectronically controlled shutter blade between the lamp and the end ofthe bundle, which can turn the light through the bundle on and off. Thebundle is 1 meter long, and the optical output is fitted into a lenstube that has a quartz lens to focus the UV to a spot. The light source26 is capable of producing a spot somewhat less than 1 mm in diameter,with a long wave UV intensity of about 1 watt/cm2.

In the system of FIG. 3, means may be provided to keep the surface 23 ata constant level and to replenish this material after an object has beenremoved, so that the focus spot 27 will remain sharply in focus on afixed focus plane, thus insuring maximum resolution in forming a thinlayer along the working surface. In this regard, it is desired to shapethe focal point to provide a region of high intensity right at theworking surface 23, rapidly diverging to low intensity and therebylimiting the depth of the curing process to provide the thinnestappropriate cross-sectional laminae for the object being formed. This isbest accomplished by using a short focal length lens and bringing thesource 26 as close as possible to the working surface, so that maximumdivergence occurs in the cone of focus entering the fluid medium. Theresult is substantially enhanced resolution.

An H-P Model 9872 Digital Plotter (not shown) manufactured byHewlett-Packard, of Palo Alto, Calif., is used to move the light source26. The lens tube is attached to the pen carriage of the plotter, andthe plotter is driven by a computer 28 using normal graphic commands.The shutter is controlled by an H-P 3497A Data Acquisition/Control Unit,using computer commands.

Other physical forms of the light source 26 or its equivalent arefeasible. Scanning could be done with optical scanners, and this wouldeliminate the fiber optic bundle and the digital plotter. A UV lasermight ultimately be a better light source than a short arc lamp. Thespeed of the stereolithographic process is mainly limited by theintensity of the light source and the response of the UV curable liquid.

The elevator platform 29 is used to support and hold the object 30 beingformed, and to move it up and down as required. Typically, after a layeris formed, the object 30 is moved beyond the level of the next layer toallow the liquid 22 to flow into the momentary void at surface 23 leftwhere the solid was formed, and then it is moved back to the correctlevel for the next layer. The requirements for the elevator platform 29are that it can be moved in a programmed fashion at appropriate speeds,with adequate precision, and that it is powerful enough to handle theweight of the object 30 being formed. In addition, a manual fineadjustment of the elevator platform position is useful during the set-upphase and when the object is being removed.

The elevator platform 29 for the embodiment of FIG. 3 is a platformattached to an analog plotter (not shown). This plotter is driven by theH-P 3497A Data Acquisition/Control Unit with its internal digital toanalog converter, under program control of the computer 28.

The computer 28 in the stereolithographic system of the presentinvention has two basic functions. The first is to help the operatordesign the three-dimensional object in a way that it can be made. Thesecond is to translate the design into commands that are appropriate forthe other stereolithographic components, and to deliver these commandsin a way so that the object is formed. In some applications, the objectdesign will exist, and the only function of the computer will be todeliver the appropriate commands.

In an ideal situation, the operator will be able to design the objectand view it three-dimensionally on the CRT screen of the computer 28.When he is finished with the design, he will instruct the computer 28 tomake the object, and the computer will issue the appropriateinstructions to the stereolithographic components.

In a present working embodiment of the invention, the computer 28 is anH-P 9816, using a Basic Operating System. A typical program is shown inAppendix A. In this system, the operator programs using H-P GraphicLanguage, the command structure for the 3497A, plus the Basic Languagecommands. The operator also must set the appropriate exposure times andrates for the UV curable material. To operate the system an image of theobject is created and a program is written to drive the stereolithographto make that object.

The elevator platform 29 can be mechanical, pneumatic, hydraulic, orelectrical and may also use optical or electronic feedback to preciselycontrol its position. The elevator platform 29 is typically fabricatedof either glass or aluminum, but any material to which the cured plasticmaterial will adhere is suitable.

In some cases, the computer 28 becomes unnecessary and simpler dedicatedprogramming devices can be used, particularly where only simply shapedobjects are to be formed. Alternatively, the computer control system 28can be simply executing instructions that were generated by another,more complex, computer. This might be the case where severalstereolithography units are used to produce objects, and another deviceis used to initially design the objects to be formed.

A computer controlled pump (not shown) may be used to maintain aconstant level of the liquid 22 at the working surface 23. Appropriatelevel detection system and feedback networks, well known in the art, canbe used to drive a fluid pump or a liquid displacement device, such as asolid rod (not shown) which is moved out of the fluid medium as theelevator platform is moved further into the fluid medium, to offsetchanges in fluid volume and maintain constant fluid level at the surface23. Alternatively, the source 26 can be moved relative to the sensedlevel 23 and automatically maintain sharp focus at the working surface23. All of these alternatives can be readily achieved by conventionalsoftware operating in conjunction with the computer control system 28.

After the three-dimensional object 30 has been formed, the elevatorplatform 29 is raised and the object is removed from the platform.Typically, the object is then ultrasonically rinsed in a solvent, suchas acetone, that dissolves the liquid state of the uncured fluid mediumand not the cured solid state medium. The object 30 is then placed underan intense ultraviolet floodlight, typically a 200 watt per inch UV curelamp, to complete the curing process.

In addition, there may be several containers 21 used in the practice ofthe invention, each container having a different type of curablematerial that can be automatically selected by the stereolithographicsystem. In this regard, the various materials might provide plastics ofdifferent colors, or have both insulating and conducting materialavailable for the various layers of electronic products.

Referring now more particularly to the remaining drawings, in connectionwith various alternative embodiments of the invention, like referencenumerals throughout the various figures of the drawings denote like orcorresponding parts as those previously discussed in connection with thepreferred embodiment of the invention shown in FIG. 3.

As will be apparent from FIG. 4 of the drawings, there is shown analternate configuration for a stereolithograph wherein the UV curableliquid 22 or the like floats on a heavier UV transparent liquid 32 whichis non-miscible and non-wetting with the curable liquid 22. By way ofexample, ethylene glycol or heavy water are suitable for theintermediate liquid layer 32. In the system of FIG. 4, thethree-dimensional object 30 is pulled up from the liquid 22, rather thandown and further into the liquid medium, as shown in the system of FIG.3.

The UV light source 26 in FIG. 4 focuses the spot 27 at the interfacebetween the liquid 22 and the non-miscible intermediate liquid layer 32,the UV radiation passing through a suitable UV transparent window 33, ofquartz or the like, supported at the bottom of the container 21. Thecurable liquid 22 is provided in a very thin layer over the non-misciblelayer 32 and thereby has the advantage of limiting layer thicknessdirectly, rather than relying solely upon absorption and the like tolimit the depth of curing, since ideally an ultrathin lamina is to beprovided. Hence, the region of formation will be more sharply definedand some surfaces will be formed smoother with the system of FIG. 4 thanwith that of FIG. 3. In addition, a smaller volume of UV curable liquid22 is required, and the substitution of one curable material for anotheris easier.

The system of FIG. 5 is similar to that of FIG. 3, but the movable UVlight source 26 is eliminated and a collimated, broad UV light source 35and suitable apertured mask 36 is substituted for the programmed source26 and focused spot 27. The apertured mask 36 is placed as close aspossible to the working surface 23, and collimated light from the UVsource 35 passes through the mask 36 to expose the working surface 23,thereby creating successive adjacent laminae, as in the embodiments ofFIGS. 3 and 4. However, the use of a fixed mask 36 providesthree-dimensional objects with a constant cross-sectional shape.Whenever that cross-sectional shape is to be changed, a new mask 36 forthat particular cross-sectional shape must be substituted and properlyaligned. Of course, the masks can be automatically changed by providinga web of masks (not shown) which are successively moved into alignmentwith with the surface 23.

FIG. 6 of the drawings again provides a stereolithographic systemconfiguration similar to that previously described in connection withFIG. 3. However, a cathode ray tube (CRT) 38, fiber optic faceplate 39and water (or other) release layer 40 are provided as a substitute forthe light source 26 and focus spot 27. Hence, the graphic image providedby a computer 28 to the CRT 38 produces the forming image upon the UVemitting phosphor face of the tube where it passes through the fiberoptic layer 39 and release layer 40 to the working surface 23 of thefluid medium 22. In all other respects, the system of FIG. 6 formssuccessive cross-sectional laminae defining the desiredthree-dimensional object to be formed, in exactly the same way as theembodiments of the invention previously discussed.

FIGS. 7 and 8 illustrate an embodiment of a stereolithographic systemwherein the elevator platform 29 has additional degrees of freedom, sothat different faces of the object 30 may be exposed for alternatemethods of construction. Similarly, the stereolithography process may beutilized as an "add on" process where the elevator platform 29 will beused to pick up and locate another part for supplementarystereolithographic processing. In this regard, the systems shown inFIGS. 7 and 8 are identical to that of FIG. 3 with the exception of theelevator platform 29 which, in the systems of FIGS. 7 and 8 have asecond degree of freedom via manual or automatically controlled rotationabout a pivot pin or hinge member 42. In this regard, FIG. 7 illustratesan adjustable elevator platform 29a in the conventional position, whileFIG. 8 shows the platform 29a rotated 90° so that a supplementary,stereolithographically formed structure 41 can be selectively formed asan addition to one side of the three-dimensional object 30.

A commercial stereolithography system will have additional componentsand subsystems besides those previously shown in connection with theschematically depicted systems of FIGS. 3-8. For example, the commercialsystem would also have a frame and housing, and a control panel. Itshould have means to shield the operator from excess UV and visiblelight, and it may also have means to allow viewing of the object 30while it is being formed. Commercial units will provide safety means forcontrolling ozone and noxious fumes, as well as conventional highvoltage safety protection and interlocks. Such commercial units willalso have means to effectively shield the sensitive electronics fromelectronic noise sources.

As previously mentioned, a number of other possible apparatus may beutilized to practice the stereolithographic method of the presentinvention. For example, an electron source, a visible light source, oran x-ray source or other radiation source could be substituted for theUV light source 26, along with appropriate fluid media which are curedin response to these particular forms of reactive stimulation. Forexample, alphaoctadecylacrylic acid that has been slightlyprepolymerized with UV light can be polymerized with an electron beam.Similarly, poly (2,3-dichloro-1-propyl acrylate) can be polymerized withan x-ray beam.

The stereolithographic method and apparatus of the present invention hasmany advantages over currently used methods for producing plasticobjects. The method of the present invention avoids the need ofproducing design layouts and drawings, and of producing tooling drawingsand tooling. The designer can work directly with the computer and astereolithographic device, and when he is satisfied with the design asdisplayed on the output screen of the computer, he can fabricate a partfor direct examination. If the design has to be modified, it can beeasily done through the computer, and then another part can be made toverify that the change was correct. If the design calls for severalparts with interacting design parameters, the method of the inventionbecomes even more useful because all of the part designs can be quicklychanged and made again so that the total assembly can be made andexamined, repeatedly if necessary.

After the design is complete, part production can begin immediately, sothat the weeks and months between design and production are avoided.Ultimate production rates and parts costs should be similar to currentinjection molding costs for short run production, with even lower laborcosts than those associated with injection molding. Injection molding iseconomical only when large numbers of identical parts are required.Stereolithography is useful for short run production because the needfor tooling is eliminated and production set-up time is minimal.Likewise, design changes and custom parts are easily provided using thetechnique. Because of the ease of making parts, stereolithography canallow plastic parts to be used in many places where metal or othermaterial parts are now used. Moreover, it allows plastic models ofobjects to be quickly and economically provided, prior to the decisionto make more expensive metal or other material parts.

It will be apparent from the foregoing that, while a variety ofstereolithographic systems have been disclosed for the practice of thepresent invention, they all have in common the concept of drawing upon asubstantially two-dimensional surface and extracting a three-dimensionalobject from that surface.

The present invention satisfies a long existing need in the art for aCAD and CAM system capable of rapidly, reliably, accurately andeconomically designing and fabricating three-dimensional plastic partsand the like.

It will be apparent from the foregoing that, while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

I claim:
 1. An apparatus for producing a three-dimensional object from a medium capable of solidification when subjected to synergistic stimulation, said apparatus comprising:a container for holding said medium, said medium having a surface; a platform relatively moveable with respect to said surface for supporting said object as it is being produced and for relatively separating said surface and any previously formed lamina to allow formation of successive layers of medium; means for selectively exposing said successive layers of medium to a beam of synergistic stimulation to form successive laminae integral with any previously formed laminae; and means for scanning at least one layer of said medium, during the formation of at least one lamina, according to a plurality of successive parallel lines, wherein the scanning direction of each successively scanned parallel line is antiparallel to the scanning direction of the immediately preceding scanned line in the succession.
 2. A method of producing a three-dimensional object from a medium capable of solidification when subjected to synergistic stimulation, said method comprising the steps of:a. providing data representing the three-dimensional object; b. providing said medium; c. forming a layer of medium in preparation for forming a lamina of said object, said layer of medium having a surface; d. selectively exposing said surface of said layer of medium to a beam of synergistic stimulation in accordance with said data to form said lamina integral with any previously formed lamina; e. repeating steps (c) and (d) a plurality of times to form said three-dimensional object from a plurality of solidified and adhered laminae; and f. wherein said step of exposing comprises scanning at least a portion of one layer according to a plurality of successively scanned parallel lines wherein the scanning direction of each successively scanned parallel line is antiparallel to the scanning direction of the immediately preceding scanned line in the succession.
 3. The method of claim 2 wherein the plurality of parallel lines is a group of parallel lines, wherein each line has two sides, and wherein at least some lines are bounded on both sides by other lines in the group.
 4. The method of claim 3 wherein the medium is a photopolymer.
 5. An apparatus for producing a three-dimensional object from a medium capable of solidification when subjected to a beam of prescribed radiation, said apparatus comprising:a container for holding said medium, said medium having a surface; a platform relatively moveable with respect to said surface for supporting said object as it is being produced and for relatively separating said surface and any previously formed lamina to allow formation of successive layers of medium; means for selectively exposing said successive layers of medium to said beam of prescribed radiation to form successive laminae integral with any previously formed laminae; means for scanning at least one layer of aid medium, during formation of at least a portion of at least one lamina, according to a plurality of successively scanned parallel lines wherein the scanning direction of each successively scanned parallel line is antiparallel to the scanning direction of the immediately preceding scanned line in the succession.
 6. A method of producing a three-dimensional object from a medium capable of solidification upon exposure to prescribed radiation, said method comprising the steps of:a. providing data representing the three-dimensional object; b. providing said medium; c. forming a layer of medium in preparation for forming a lamina of said object, said layer of medium having a surface; d. selectively exposing said surface of said layer of medium to a beam of prescribed radiation according to said data to form said lamina integral with any previously formed lamina; e. repeating steps (c) and (d) a plurality of times to form said three-dimensional object from a plurality of solidified and adhered laminae; and f. wherein said step of selectively exposing, during formation of at least one lamina, includes exposing said surface to a plurality of successively scanned parallel lines wherein the scanning direction of each successively scanned parallel line is antiparallel to the scanning direction of the immediately preceding scanned line in the succession.
 7. The method of claim 6 wherein the plurality of parallel lines is a group of parallel lines, wherein each line has two sides, and wherein at least some lines are bounded on both sides by other lines in the group.
 8. The method of claim 7 wherein the medium is a photopolymer. 